FIGS. 1 to 3 show typical examples of a conventional rotary pump and operations thereof, schematically. In FIG. 1, a vane type rotary pump is shown, in which an inner wall 102 of a housing is eccentric with respect to a center 101 of a rotary shaft so that an area in a plane orthogonal to the rotary shaft defined by an outer wall 103 of a rotor, the inner wall 102 and adjacent vanes 104 increases and decreases periodically with rotation of the pump device. FIG. 2 shows a non-circular rotor type rotary pump in which a rotor and a housing move relatively while they are proximate to each other or in contact with each other at at least two points on a locus curve which is deviated from a coaxial circle with a center 201 of a rotary shaft according to a fixed rule so that an area in a plane orthogonal to the rotary shaft and defined by an outer wall 203 of the rotor and an inner wall 202 of the housing increases and decreases periodically with rotation of the device. A rotary pump shown in FIG. 3 is of a scroll type which includes a stationary scroll 302 and an orbiting scroll 303 which orbits along a predetermined orbit with respect to a center 301 of a rotary shaft so that areas a to e defined between the scrolls in a plane orthogonal to the rotary shaft are increased and decreased periodically while moving spirally. In these typical examples of conventional rotary pumps, the component which performs a pump action has a configuration eccentric with respect to a rotary shaft, rotates eccentrically, has a non-circular configuration other than a coaxial circular with the rotary shaft or moves in special mode such as spiral movement, or employs a combination of two or more of those mentioned above.
Therefore, there are technical problems such as, in these conventional rotary pumps performing eccentric movement, difficulties of minimization of friction between a component which moves eccentrically and a component which does not move eccentrically and maximization of friction durabilities thereof and, in those having a non-circular component, difficulties in machining and in increasing a configuration precision. Since these problems lead to a friction problem and a sealing problem for fluid which affect a performance of the rotary pump directly, a high degree of control technique is necessary in producing such device practically, resulting in a high manufacturing cost.
This invention was made in view of resolution of these problems and an object of this invention is to obtain a rotary pump by which a friction loss can be minimized, machinings of a piston and a cylinder are easy, a loss of driving mechanism can be reduced and a loss of inertia can be restricted.